Patent literature 1: JP 4483298 B2
Patent literature 2: JP 2009-17707 A
Conventionally, a motor control apparatus has been known. The motor control apparatus estimates a temperature of electronic components (for example, elements) configuring a motor coil or an electric power converter. And the motor control apparatus limits a current command value to prevent overheating. A temperature estimation method of a motor coil disclosed in Patent literature 1 inputs a time average of an integrated value of a current squared value, the current being supplied to the motor coil, to a primary delay function. The temperature estimation method estimates the temperature of the motor coil. Patent literature 2 calculates estimated temperature in each phase (also referred to as an each phase estimated temperature) by adding a temperature measurement result of an inverter measured by a temperature sensor before starting a motor rotation to a predicted calorific value that is estimated based on each phase current when rotating a motor.
The temperature estimation method in patent literature 1 estimates the temperature of the motor coil. This method may be also used in a temperature estimation of an electric power converter. In combination with the technique disclosed in patent literature 2, a configuration of adding “the primary delay response obtained by inputting the time average of the integrated value of the current square value to a primary delay arithmetic unit” to “the temperature sensor value” and of estimating a temperature may be supposed. The inventor of the present application has found the following difficulty regarding the conventional technology.
According to a conventional technology, since the temperature is estimated from (i) the square value of the current supplied to the electric power converter and (ii) the value of the temperature sensor (also referred to as a temperature sensor value), the self-heat generation of the respective components before supplying the current to the electric power converter, and the amount of heat received from heat generation of other components may not be estimated in principle. When the amount of heat generation is uniformly added and corrected, a current may be excessively limited with a greatly expected temperature rise (that is, the temperature rise is estimated too much). The performance of the motor may not be effectively exhibited.
It is supposed that the temperature of the element (for example, IC) whose power consumption changes according to a power supply voltage is estimated by an addition of an offset temperature. When the offset temperature is set as a fixed value, a change in the supply voltage may not be reflected on the offset temperature. When the largest supply voltage is expected and the offset temperature is set from a viewpoint of fail-safe, the offset temperature may be excessively largely expected when the supply voltage is low. Thus, the current is excessively limited, and the performance of the motor may not be effectively exhibited.
When a temperature of a switching element in the electric power converter is estimated, since a duty changes as an input voltage of the electric power converter changes (for example, when the input voltage becomes higher, an on-duty of an upper arm element to the identical output is decreased), a heat generation state of the switching element may change. Therefore, when a gain and a time constant of the primary delay response are set as fixed values, it may not be possible to estimate the temperature in high precision.
When the duty of the switching element changes under a PWM (pulse width modulation) control, an on-time ratio allowing a current flow changes (for example, a temperature of the switching element with large on-duty increases in a motor lock state). Therefore, the sufficient estimation precision may not be obtained in a configuration without taking the duty into consideration.
For example, it is supposed that, in the PWM control of a three-phase motor, a motor control apparatus switches between three-phase modulation and two-phase modulation according to a voltage utilization rate. In that case, when the temperature is estimated under a condition of an electric angle range in which a duty is fixed to an upper limit by upper flatbed two-phase modulation for an upper arm element, and an electric angle range in which the duty is fixed to a lower limit by lower flatbed two-phase modulation for a lower arm element, the current may be excessively limited in the other electric angle range or the three-phase modulation. Thus, the performance of the motor may not be effectively exhibited.
In the switching element of each phase in a multi-phase motor, a difference (variation) in heat resistance or heat capacity of heat radiation from a junction of the switch element of each phase to a heat sink may occur due to a hardware factor such as a heat sink shape or a heat radiation structure. A heat generation difference may occur. In that case, when the temperature is estimated with reference to a phase having the largest heat resistance (temperature is liable to most increase) from the viewpoint of device protection, the temperature rise may be excessively largely expected for a phase relatively small in the heat resistance (temperature is difficult to increase). Thus, the current may be excessively limited, and the performance of the motor may not be effectively exhibited.
Thus, considering the change in the external factors or the control conditions, temperature estimation sufficiently high in precision cannot be performed conventionally. The performance of the motor may not be effectively exhibited. When the required torque is secured even under the current limit, a rating of components or a body size of the heat sink may be increased.